U.S. patent number 7,653,308 [Application Number 11/504,741] was granted by the patent office on 2010-01-26 for path routing computation method and optical communication network applying path routing computation method.
This patent grant is currently assigned to Fujitsu Limited. Invention is credited to Yasuki Fujii, Shinya Kanoh, Keiji Miyazaki, Akira Nagata.
United States Patent |
7,653,308 |
Miyazaki , et al. |
January 26, 2010 |
Path routing computation method and optical communication network
applying path routing computation method
Abstract
A path routing computation method enables reduction of the
memory capacity for path routing computation. The method is
characterized in that a wavelength convertible subnetwork in which
paths are connected in a mesh form; a first and second wavelength
inconvertible subnetworks have a starting point node and an end
point node, respectively, and include a plurality of nodes and
connected via the wavelength convertible subnetwork, and out of the
nodes constituting the first and second wavelength inconvertible
subnetworks, a node has a port connected to the wavelength
convertible subnetwork is defined as a border node, and the method
includes the steps of: obtaining, for the first wavelength
inconvertible subnetwork, a path from the starting point node to a
border node in the first subnetwork; and obtaining, for the second
wavelength inconvertible subnetwork, a path from the end point node
to a border node in the second wavelength inconvertible
subnetwork.
Inventors: |
Miyazaki; Keiji (Kawasaki,
JP), Fujii; Yasuki (Kawasaki, JP), Kanoh;
Shinya (Kawasaki, JP), Nagata; Akira (Kawasaki,
JP) |
Assignee: |
Fujitsu Limited (Kawasaki,
JP)
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Family
ID: |
38479056 |
Appl.
No.: |
11/504,741 |
Filed: |
August 15, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070212068 A1 |
Sep 13, 2007 |
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Foreign Application Priority Data
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Mar 8, 2006 [JP] |
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2006-062010 |
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Current U.S.
Class: |
398/58; 398/59;
398/57 |
Current CPC
Class: |
H04J
14/0283 (20130101); H04J 14/0286 (20130101); H04J
14/0284 (20130101); H04J 14/0227 (20130101); H04J
14/0241 (20130101) |
Current International
Class: |
H04J
14/00 (20060101) |
Field of
Search: |
;398/2-5,57,58,59
;370/351,400,404,405,406 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2002-271372 |
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Sep 2002 |
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JP |
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2003-198609 |
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Jul 2003 |
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JP |
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Primary Examiner: Singh; Dalzid
Attorney, Agent or Firm: Katten Muchin Rosenman LLP
Claims
What is claimed is:
1. A path routing computation method in an optical communication
network including a wavelength convertible subnetwork in which
paths are connected in the form of a mesh, a first wavelength
inconvertible subnetwork having a starting point node, and a second
wavelength inconvertible subnetwork having an end point node, the
first and second wavelength inconvertible subnetworks being
connected via the wavelength convertible subnetwork, wherein out of
the nodes constituting the first and second wavelength
inconvertible subnetworks, a node having a port connected to the
wavelength convertible subnetwork is defined as a border node, the
path routing computation method comprising: obtaining, for the
first wavelength inconvertible subnetwork, a path from the starting
point node to a border node in the first subnetwork; and obtaining,
for the second wavelength inconvertible subnetwork, a path from the
end point node to a border node in the second wavelength
inconvertible subnetwork.
2. The path routing computation method according to claim 1,
wherein when the end point node is searched by the step of
obtaining, for the first wavelength inconvertible subnetwork, a
path from the starting point node to a border node in the first
wavelength inconvertible subnetwork, the routing computation is
ended.
3. The path routing computation method according to claim 1,
wherein if a border node, which is searched by the step of
obtaining, for the first wavelength inconvertible subnetwork, a
path from the starting point node to a border node in the first
wavelength inconvertible subnetwork, does not have a border node
which is searched by the step of obtaining, for the second
wavelength inconvertible subnetwork, a path from the end point node
to a border node in the second wavelength inconvertible subnetwork,
routing computation is further performed alternately for the first
wavelength inconvertible subnetwork and the second wavelength
inconvertible subnetwork until the same border node is searched,
with the searched border nodes as original points.
4. The path routing computation method according to claim 3,
wherein a path of the lowest cost in a combination of the paths
searched for the first wavelength inconvertible subnetwork and the
second wavelength inconvertible subnetwork is taken as a
shortest-distance path to be obtained.
5. The path routing computation method according to claim 1,
wherein a path of the lowest cost in a combination of the paths
searched for the first wavelength inconvertible subnetwork and the
second wavelength inconvertible subnetwork is taken as a
shortest-distance path to be obtained.
6. A path routing computation method in an optical communication
network including a wavelength convertible subnetwork in which
paths are connected in the form of a mesh, a first wavelength
inconvertible subnetwork having a starting point node, and a second
wavelength inconvertible subnetwork having an end point node, the
first and second wavelength inconvertible subnetworks being
connected via the wavelength convertible subnetwork, wherein out of
the nodes constituting the first and second wavelength
inconvertible subnetworks, a node having a port connected to the
wavelength convertible subnetwork is defined as a border node, the
path routing computation method comprising: obtaining, for the
first wavelength inconvertible subnetwork, a path from the starting
point node to a border node in the first subnetwork; and obtaining,
for the second wavelength inconvertible subnetwork, a path from the
end point node to a border node in the second wavelength
inconvertible subnetwork, wherein a path of the lowest cost in a
combination of the paths searched for the first wavelength
inconvertible subnetwork and the second wavelength inconvertible
subnetwork is taken as a shortest-distance path to be obtained and,
wherein the shortest path between the starting point node and the
end point node is obtained as a predetermined shortest path in
advance without considering wavelength limiting conditions, and the
obtained shortest path is compared with the predetermined shortest
path to determine whether to perform further routing search, on the
basis of a predetermined rate with respect to the predetermined
shortest path.
7. A path routing computation method in an optical communication
network including a wavelength convertible subnetwork in which
paths are connected in the form of a mesh, a first wavelength
inconvertible subnetwork having a starting point node, and a second
wavelength inconvertible subnetwork having an end point node, the
first and second wavelength inconvertible subnetworks being
connected via the wavelength convertible subnetwork, wherein out of
the nodes constituting the first and second wavelength
inconvertible subnetworks, a node having a port connected to the
wavelength convertible subnetwork is defined as a border node, the
path routing computation method comprising: obtaining, for the
first wavelength inconvertible subnetwork, a path from the starting
point node to a border node in the first subnetwork; and obtaining,
for the second wavelength inconvertible subnetwork, a path from the
end point node to a border node in the second wavelength
inconvertible subnetwork, wherein if a border node, which is
searched by the step of obtaining, for the first wavelength
inconvertible subnetwork, a path from the starting point node to a
border node in the first wavelength inconvertible subnetwork, does
not have a border node which is searched by the step of obtaining,
for the second wavelength inconvertible subnetwork, a path from the
end point node to a border node in the second wavelength
inconvertible subnetwork, routing computation is further performed
alternately for the first wavelength inconvertible subnetwork and
the second wavelength inconvertible subnetwork until the same
border node is searched, with the searched border nodes as original
points, wherein a path of the lowest cost in a combination of the
paths searched for the first wavelength inconvertible subnetwork
and the second wavelength inconvertible subnetwork is taken as a
shortest-distance path to be obtained, and wherein the shortest
path between the starting point node and the end point node is
obtained as a predetermined shortest path in advance without
considering wavelength limiting conditions, and the obtained
shortest path is compared with the predetermined shortest path to
determine whether to perform further routing search, on the basis
of a predetermined rate with respect to the predetermined shortest
path.
8. An optical communication network system comprising: a wavelength
convertible subnetwork in which paths are connected in the form of
a mesh; a first wavelength inconvertible subnetwork including a
plurality of nodes, one of which is a starting point node and
transmitting signals at a fixed wavelength; and a second wavelength
inconvertible subnetwork including a plurality of nodes, one of
which is an end point node and transmitting signals at a fixed
wavelength the first and second wavelength inconvertible
subnetworks being connected via the wavelength convertible
subnetwork, wherein, out of the nodes constituting the first and
second wavelength inconvertible subnetworks, a node having a port
connected to the wavelength convertible subnetwork is defined as a
border node, and a path from the starting point node to a border
node in the first wavelength inconvertible subnetwork and a path
from the end point node to a border node in the second wavelength
inconvertible subnetwork are obtained to set a path of the lowest
cost, which is obtained in a combination of the paths searched for
the first wavelength inconvertible subnetwork and the second
wavelength inconvertible subnetwork, as a path from the starting
point node to the end point node through the wavelength convertible
subnetwork.
9. In an optical communication network including a wavelength
convertible subnetwork in which paths are connected in the form of
a mesh, and first and second wavelength inconvertible subnetworks
connected via the wavelength convertible subnetwork, a node device
which is connected to the wavelength convertible network as a
border node and which is one of a plurality of node devices
constituting the first and second wavelength inconvertible
subnetworks, wherein address information and link information as
topology information is notified in order to search for and set a
path from a starting point node of the first wavelength
inconvertible subnetwork to an end point node, of the second
wavelength inconvertible subnetwork, and wherein the topology
information includes information indicating that own node device is
a border node if the information is notified from the border node.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from the prior Japanese Patent Application No. 2006-62010, filed on
Mar. 8, 2006, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a path routing computation method
and an optical communication network applying the path routing
computation method. Particularly, the present invention relates to
a path routing computation method for setting a path in a network
connected to wavelength convertible and inconvertible subnetworks
constituted by Reconfigurable Optical Add/Drop Multiplexing (ROADM)
devices.
2. Description of the Related Art
Regarding the forms of optical communication networks, there is a
ROADM ring network in which ROADM devices present in nodes are
connected to form a ring. In the example shown in FIG. 1 a ROADM
ring network is constituted such that three ROADM rings 1, 2, and 3
are connected with each other as subnetworks. The inside of each of
the ROADM rings is fixed to a transmission wavelength for fixation.
Specifically, wavelengths are fixed so that wavelength conversion
cannot be performed.
FIG. 2 is a configuration example of a ROADM device having, for
example, a ring 1. The inside of the ring 1 is constituted such
that a wavelength signal with a wavelength of .lamda.1 through
.lamda.10 is transmitted, and that an optical signal having a
specific wavelength is added and dropped from or to a tributary
portion 13 through a switch 12a, 12b.
Therefore, in FIG. 1, when an optical signal with a wavelength 1 is
transmitted from a ROADM device of a node A as a starting point to
a ROADM device of a node Z as an end point, the inside the ring 1
is transmitted at the fixed wavelength 1 as it is, and then the
wavelength 1 is converted at a node in the ring 3 and transmitted
at a wavelength 5 fixed inside the ring 3.
In this manner, the ROADM ring network has a restriction in the
transmission wavelengths, and further has a restriction in
transmittable wavelengths based on deterioration and the like in
transmission of signals in the nodes through which the signals
pass.
On the other hand, as other form of an optical communication
network, there is a WDM network in which paths are connected in the
form of a mesh. This is a wavelength convertible network which does
not have a restriction that the transmission wavelengths are fixed
as in the ROADM ring network shown in FIG. 1 above
(non-blocking).
FIG. 3 shows a network in which wavelength inconvertible ROADM ring
networks 101 and 102 as subnetworks are connected to a wavelength
convertible WDM network 100 described above.
In the networks shown in FIG. 1 and FIG. 3, a routing path needs to
be set up in order to transmit an optical signal from a starting
point node to a destination (end point) node.
In order to set up a routing path, a routing protocol is used
beforehand so that network information such as limiting conditions
is notified between the nodes, and the network information such as
the notified limiting conditions and costs (a random criterion
which is set by a user in advance, a numeric value based on, for
example, the path selection priority, and the like) between the
nodes is stored in a routing table provided in a ROADM device of
each node.
In a distributed processing system, in a ROADM device of a node as
the starting point which receives a path set-up request, path
routing computation for obtaining a path MSL where a routable cost
is the minimum is carried out on the basis of the information
stored in the routing table.
Alternatively, in a centralized data processing system, network
information is stored in a network management system (NMS) for
centrally controlling the states of the nodes on the network. On
the basis of such network information, the NMS, which receives a
request via the ROADM device of the starting point node, performs
path routing computation.
As a conventional technology related to path routing computation,
there is the invention described in Japanese Patent Application
Laid-Open No. 2003-198609. An object of the invention described in
Japanese Patent Application Laid-Open No. 2003-198609 is to perform
routing computation which does not fail by depending on the
restriction on the connectivity between cross-connect devices in an
optical communication network.
Further, a virtual neighbor link is defined in backbone, and an
optical path routing between a starting point and an end point is
computed using the information on the virtual neighbor link.
Moreover, the information described in Japanese Patent Application
Laid-Open No. 2002-291372 describes a path routing computation
system in which is used a boundary node for performing path
setting.
Now, suppose that there is a network configuration as shown in FIG.
4. In this network, ROADM rings R1 through R6 are connected to a
mesh network 100 in a multi-stage manner. In such a configuration,
the mesh network 100 does not have restrictions in wavelengths. On
the other hand, the ROADM rings R1 through R3 and R4 through R6
connected to the mesh network 100 are, as described in FIG. 1, have
restrictions in wavelengths and the like.
Regarding path routing computation for path setting, for the ring
network in which are connected the ROADM rings R1 through R3 on the
starting point node A side, which are connected to the mesh network
100, it is only necessary to consider only a starting point
wavelength of .lamda.1 from the starting point node A, as in the
explanation of FIG. 1.
However, in the plurality of ROADM rings R4 through R6 on the
output side of the mesh network 100, a plurality of wavelengths
need to be considered. In this case, the output side of the mesh
network 100 has paths in usable wavelengths between .lamda.5
through 15 and in usable wavelengths between .lamda.12 through 20,
thus a candidate wavelength cannot be specified.
It is necessary to determine which one of the transponders of the
ROADM devices is selected and used to obtain a path of the shortest
distance or the lowest cost.
In a method for such a purpose, it is necessary to generate a
wavelength graph for each wavelength and search for the shortest
distance on the basis of the wavelength graph. The wavelength graph
is information obtained by using a wavelength fixed for each link,
to define a connection between the links. Therefore, a wavelength
graph corresponding to each wavelength needs to be created.
Furthermore, generally a scale required for searching for a path is
considered to be proportional to the square of the number of nodes.
Therefore, there is a problem that the memory capacity required for
routing computation becomes extremely large if the number of
multiplexed wavelengths increases.
SUMMARY OF THE INVENTION
In view of the above points, an object of the present invention is
to provide a path routing computation method and an optical
communication network system which applies such a method, the path
routing computation method being capable of reducing the memory
capacity for path routing computation without increasing the size
of a path routing computation graph in proportion to the number of
multiplexed wavelengths even if the number of multiplexed
wavelengths increases, and further capable of reducing the time
required in routing computation, even if the number of routing
computation times increases.
A first aspect of the present invention for achieving the above
object is a path routing computation method in an optical
communication network having: a wavelength convertible subnetwork
in which paths are connected in the form of a mesh; a first
wavelength inconvertible subnetwork having a starting point node;
and a second wavelength inconvertible subnetwork having an end
point node, the first wavelength inconvertible subnetwork having a
starting point node and the second wavelength inconvertible
subnetwork having an end point node having a plurality of nodes and
being connected via the wavelength convertible subnetwork, wherein,
out of the nodes constituting the first and second wavelength
inconvertible subnetworks, a node having a port connected to the
wavelength convertible subnetwork is defined as a border node, and
wherein the method has the steps of: obtaining, for the first
wavelength inconvertible subnetwork, a path from the starting point
node to a border node in the first subnetwork; and obtaining, for
the second wavelength inconvertible subnetwork, a path from the end
point node to a border node in the second wavelength inconvertible
subnetwork.
The first aspect can be configured such that, when the end point
node is searched by the step of obtaining, for the first wavelength
inconvertible subnetwork, a path from the starting point node to a
border node in the first wavelength inconvertible subnetwork, the
routing computation is ended.
The first aspect can be configured such that, if a border node,
which is searched by the step of obtaining, for the first
wavelength inconvertible subnetwork, a path from the starting point
node to a border node in the first wavelength inconvertible
subnetwork, does not have a border node which is searched by the
step of obtaining, for the second wavelength inconvertible
subnetwork, a path from the end point node to a border node in the
second wavelength inconvertible subnetwork, routing computation is
further performed alternately for the first wavelength
inconvertible subnetwork and the second wavelength inconvertible
subnetwork until the same border node is searched, with the
searched border nodes as original points.
Moreover, in the above description, a path of the lowest cost in a
combination of the paths searched for the first wavelength
inconvertible subnetwork and the second wavelength inconvertible
subnetwork is taken as a shortest-distance path to be obtained.
Furthermore, wherein the shortest path between the starting point
node and the end point node is obtained as a predetermined shortest
path in advance without considering wavelength limiting conditions,
and the obtained shortest path is compared with the predetermined
shortest path to determine whether to perform further routing
search, on the basis of a predetermined rate with respect to the
predetermined shortest path.
Further, a second aspect of the present invention for achieving the
above object is an optical communication network system, having: a
wavelength convertible subnetwork in which paths are connected in
the form of a mesh; a first wavelength inconvertible subnetwork
having a starting point node; and a second wavelength inconvertible
subnetwork having an end point node, the first and second
subnetworks having a plurality of nodes in the form of a ring and
transmitting signals at a fixed wavelength, wherein, out of the
nodes constituting the first and second wavelength inconvertible
subnetworks, a node having a port connected to the wavelength
convertible subnetwork is defined as a border node, and a path to a
border node in the first wavelength inconvertible subnetwork in the
starting point node and a path from the end point node in the
second wavelength inconvertible subnetwork to a border node in the
second wavelength inconvertible subnetwork are obtained to set a
path of the lowest cost, which is obtained in a combination of the
paths searched for the first wavelength inconvertible subnetwork
and the second wavelength inconvertible subnetwork, as a path from
the starting point node to the end point node.
In addition, a third aspect of the present invention for achieving
the above object is a node device which is connected to a
wavelength convertible network and which constitutes a wavelength
inconvertible subnetwork, out of a plurality of node devices each
of which notifies address information and link information as
topology information in order to search for and set a path from a
starting point node to an end point node in a subnetwork having the
plurality of node devices, wherein the information to be notified
as the topology information includes information indicating that a
home node of each of the node devices is a border node.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a figure for explaining a ROADM ring network;
FIG. 2 is a configuration example of a ROADM device constituting a
ring 1 in the network shown in FIG. 1;
FIG. 3 is a network in which a ROADM ring network 100 and a WDM
network 200 are connected to each other;
FIG. 4 is a figure showing a network configuration in which a
network with restricted wavelengths and a network with not
restricted wavelengths are connected to each other;
FIG. 5 is a figure showing a configuration example of a network of
a first embodiment of the present invention;
FIG. 6 is a figure for explaining notification of a border
node;
FIG. 7 is a block diagram of a configuration example of a node
device;
FIG. 8 is a figure showing a configuration example of a network of
a second embodiment of the present invention;
FIG. 9 is a figure showing an example of link information when a
routing protocol corresponding to the embodiment of FIG. 8 is
used;
FIG. 10 is a figure for explaining exchange of border port
identification information;
FIG. 11 is a flowchart of a path routing computation sequence
according to the present invention;
FIG. 12 is a figure showing a state of search at the lowest cost
from a starting point node A to a border node;
FIG. 13 is a figure showing a state of search at the lowest cost
from an end point node Z to a border node;
FIG. 14 is a figure showing a state of search for the same border
node through path search from the starting point node A and from
the end point node Z;
FIG. 15 is a figure showing a path obtained from FIG. 12 through
FIG. 14, the path being the lowest cost path; and
FIG. 16 is a figure showing an example in which another network 200
is connected to the network configuration shown in FIG. 8, and a
plurality of border nodes are used as pathways.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the present invention, routing computation is
performed starting from the starting point and end point nodes to
the border nodes, and memory for routing computation can be reduced
by merging into one node. Moreover, conventionally a wavelength
graph was required to be created using exchanged network
information to perform path routing computation, whereby, for a
subnetwork without an end point as well, routing computation was
performed. However, if the network size was large, routing
computation required a long time. In the present invention, on the
other hand, a graph for routing computation, which is used in
routing computation, can be made small by using border nodes.
Accordingly, time required in routing computation can be
reduced.
Embodiments of the present invention are described hereinafter with
reference to the drawings. It should be noted that the embodiments
are explanations of the present invention to understand the present
invention, thus the technical scope of the present invention is not
to be limited to the embodiments.
FIG. 5 is a figure showing a configuration example of a network of
a first embodiment of the present invention. In FIG. 5 a ring
(single formation) 2, a ring 4, and a ring 7 as wavelength
inconvertible subnetworks are connected to a core network (mesh
network) 100 as a wavelength convertible subnetwork by one node
device, respectively.
The device connected the core network 100 is defined as a border
node. Therefore, the ring 2, ring 4, and ring 7 are connected to
the core network 100 by a border node BN1, a border node BN2, and a
border node BN3, respectively.
Moreover, the rings are configured in connection with each other by
another plurality of node devices. When a signal is inserted in a
branched manner in nodes, ROADM devices are disposed as the node
devices.
When path routing computation is carried out in a decentralized
manner, a routing protocol is used so that each node device
notifies topology information inside the network. With a general
routing protocol (OSPF-TE: Open Shortest Path Fast-Traffic
Engineering), router address information and link information are
notified, but, as shown in FIG. 6, each node device applies a
router address I with a flag II indicating whether the node is a
border node or not, and notifies this information as router address
information. If the node is a border node, flag II "1" is notified,
and if not, "0" is notified. It should be noted that the topology
information to be notified may be provided with a new field, and
information indicating whether the node is a border node or not may
be set in this field. The notified topology information is held in
each node device which receives the topology information.
In the example shown in FIG. 6, for example, as the router address
information for the border node BN1, the router address is
10.10.10.100, and a flag "1" indicating that the node is a border
node is set.
Further, when path routing computation is concentrated on an
unshown NMS (network management system) and the like, the device
information for each node device is held in the NMS.
The abovementioned link information has a link ID of a client,
wavelength information used by the client, and an ID of a link to
be connected, and is held as a client link table.
FIG. 7 is a block diagram of a configuration example of the node
device. A device monitor/control portion 20 for managing and
controlling the devices has a device management portion 21 for
performing packet generation, holding and management and the like
of set information, and an alarm monitoring portion 22 for
monitoring and notifying errors. When provided with a GMPLS control
plane, the device monitor/control portion 20 further has a GMPLS
control portion for controlling functions of signaling and the
like, which is a characteristic of the present invention. The
abovementioned notified topology information is held in the device
management portion 21.
Here, the development of the GMPLS (Generalized Multi-Protocol
Label Switching) has been promoted as a technology for implementing
routing. In optical communication networks, execution of path
routing setting in an autonomous decentralized manner using this
GMPLS has been increasingly demanded.
The GMPLS is for performing a process of determining a routing path
on the basis of a wavelength of an optical signal, and is premised
on that there is no restriction (non-blocking and the like) based
on signal transmission quality and the like.
In the configuration example of the node device shown in FIG. 7, a
switch function portion 24 for inserting a signal in a branched
manner is provided as the ROADM device shown in FIG. 2.
FIG. 8 is a figure showing a configuration example of a network of
a second embodiment of the present invention. As shown in this
network configuration of the present embodiment, a state in which
rings are connected to the core network (mesh network) 100 by two
or more node devices is referred to as "multi formation ring" as
contrasted with the abovementioned single formation.
In the network configuration shown in FIG. 8, the ring 2 and ring 4
are both connected to the core network (mesh network) 100 by two
node devices respectively, and these node devices are also defined
as border nodes BN1 through BN4.
In this embodiment as well, when path routing computation is
performed in a decentralized manner, the routing protocol is used
so that each node device notifies the topology information inside
the network. When path routing computation is performed in a
concentrated manner, the topology information is held as device
information in the NMS (network management system).
FIG. 9 shows an example of the link information when a routing
protocol corresponding to the embodiment of FIG. 8 is used. With
the general routing protocol (OSPF-TE), router address information
and link information are notified as described above, but, as shown
in FIG. 9, each node device applies, in addition to link
information I, II, a flag III indicating whether the port is a
border port or not, and notifies this information. A border port is
defined as a port in which data is sent outside from the ring.
If the port is the border port, flag III "1" is notified, and if
not, "0" is notified. In the examples shown in FIG. 9, for example,
for the link information of the border node BN1, one-to-one
connection (P-P) is stored as the link information I, 10001 as the
link ID is stored for the link information II, and 0C1921 is stored
as bandwidth information, and further a flag "1", which indicates
that the port is a border port, is set.
Here, in order to notify the link information by means of each node
device, prior to this notification it is necessary to find out
whether or not the home node in particular is a border node and
whether or not the port is a border port.
For this purpose, the link information is exchanged between the
adjacent devices y using a LMP (Link Management Protocol) or the
like. Border port identification information shown in FIG. 10 is
exchanged using this protocol or a unique protocol. As the border
port identification information, information on a device ID (I),
device type (II), and connected link ID (III) of the node, and
wavelength information in a transponder are exchanged.
In the example shown in FIG. 10, the device ID is 10011, the device
type is the ROADM device with restricted wavelength, the link ID is
20001, and the transponder wavelength is .lamda.16.
In this manner, the border port identification information is
exchanged between the devices, and, when a device with restricted
wavelength, such as the ROADM device as indicated in the device
type (II), is connected to a device with no restricted wavelength,
such as a packet cross switch (PXC), the device with restricted
wavelength is defined as a border node, and the link between the
devices is defined as a border link.
Regarding the network configuration of the first embodiment of the
present invention as shown in FIG. 5, and the network configuration
of the second embodiment of the present invention as shown in FIG.
8, embodiment methods of path routing computation according to the
present invention are described hereinafter.
In the network configurations shown in FIG. 5 and FIG. 8, the ring
networks with restricted wavelength are connected to the WDM
network 100 with no restricted wavelength. Moreover, the network
configuration shown in FIG. 8 has a disadvantage that a plurality
of wavelength routings are present on the output side of the WDM
network 100 with not restricted wavelength, as described above in
FIG. 4, thus a candidate wavelength cannot be specified.
Therefore, the present inventor has devised, according to path
routing computation of a subject network, a method of performing
routing computation from the starting point node to the end point
node, and similarly performing routing computation from the end
point node to the border node, to combine thus obtained results of
these routing computation, thereby enabling reduction of memory for
routing computation.
FIG. 11 is a flowchart of a path routing computation sequence
according to the present invention. Further, FIG. 12 through FIG.
15 are explanation drawings according to the flow sequence shown in
FIG. 11. In the flow sequence shown in FIG. 11 general Dijkstra
method is used as a general routing search sequence.
In FIG. 12, searching for a path is supposedly performed from the
node A of the ring 1 to the node Z of a ring 5 by means of routing
computation.
In the case of a decentralized processing system, this routing
computation is performed on the basis of the address information
and link information, which are previously notified to the node A
on the basis of a setting request from an originating user. In the
case of a centralization system, this routing computation is
performed by means of the NMS which is not shown. This routing
computation is executed by the GMPLS control portion 23 having the
device configuration shown in FIG. 7.
In FIG. 11, first of all, the node A is a starting point node A due
to initialization of data (step S1), thus distance 0: d(NA)=0, and
link: L(NA)=wavelength .lamda.1 are set. Other nodes are set to be
d(X)=.infin., and L(X)=null.
In this step, in judgment on whether the shortest distances to all
of the nodes are obtained (i.e. whether a set Q is empty) (step
S2), since not all shortest distances are obtained, a negative
output (NO) is obtained.
A node with the shortest distance d (u) from the set Q is the node
A, thus this node is selected (step S3).
If the shortest distances to all of the nodes are obtained (step
S2, YES), the process of searching for a path from the starting
point node A to the border node BN1 or BN3 is ended.
Subsequently, it is judged whether the node A is the final node
(border node BN1 or BN3 (step S4). If the node A is not the final
node (step S4, NO), it is judged whether a link connected to the
node A is selected (whether a link is present) (step S5). Two links
are connected to the node A, thus these two links are checked.
Then, since L (A)=wavelength .lamda.1, it is determined whether the
wavelength .lamda.1 can be used for the two links (link L10, L11,
hereinafter) (step S6).
If the wavelength .lamda.1 is contained in the usable wavelengths
of the two links L10, L11, the wavelength .lamda.1 can be used
(step S6, YES).
Next, when a destination node for one of the two links L10, L11,
i.e. the link L10, is set as BN1, d(BN1)=.infin. is compared with
d(A)+cost (L10), and the smaller cost is set to d(BN1). In this
case, d(BN1)=1, R(BN1)=NA, and L(BN1, L10)=wavelength .lamda.1 are
set.
Similarly, when a destination node for the link L11 is set as BN3,
d(BN3)=.infin. is compared with d(A)+cost (L11), and the smaller
cost is set to d(BN3). In this case, d(BN3)=1, and L(BN3,
L11)=wavelength .lamda.1 are set.
Returning to the step S2, NO is obtained from the step S5 since the
links L10, L11 are already selected in the step S5, thus the
process proceeds to a step S8 where the node A is added to S, and
then the processing is returned to the step S2.
Here, since the end point node is the border node, if a node u is
the border node, this means that the node u is the endpoint node in
the step S4 (step S4, YES). Hence, it is judged whether the node
can be branched at this node u to the end point node (step S9). If
the node can be branched (step S9, YES), the process of searching
for a path from the starting point node to the border node is ended
(see FIG. 12).
If the node cannot be branched to the end point node (step S9, NO),
the shortest distance is initialized and the processing is returned
to the step S2.
Therefore, the obtained short distance is initialized for the next
execution of shortest distance search for searching for a path from
the end point node Z to the border node (step S10). Subsequently,
the processes between the step S2 through the step S10 are executed
with the end point node Z as the initial node. Accordingly, a path
from the endpoint node Z to the border node is obtained (see FIG.
13).
At this moment, if the border nodes obtained from the starting
point A side are different from the border node obtained from the
end point Z side, that is, if the border nodes obtained from the
starting point A side do not have the border node obtained from the
end point Z side, further routing search is carried out in the
network 100 with no restricted wavelength, with the border nodes
BN1, BN3 obtained from the starting point node A as starting
points. This routing search also is executed using the Dijkstra
method.
Similarly, with the border node obtained from the end point node Z
side as a starting point, further routing search is performed in
the network 100 with no restricted wavelength.
In this manner, routing search is executed from the starting point
node A side and the end point node Z side alternately in accordance
with the flow shown in FIG. 11, and this routing search is
repeatedly performed until the same border node is reached (see
FIG. 14).
When the routing search to reach the same border node is ended in
the above-described routing search process, the paths and costs
which were obtained so far are combined, and the path of the lowest
cost is taken as the shortest distance.
FIG. 15 is a figure showing a path of the lowest cost path which is
obtained in the above manner, wherein a path on a lower side, which
runs in such a manner as node A-border node BN3-BN4-end point node
Z, is selected as the path of the lowest cost.
FIG. 16 shows an example in which another network 200 is connected
to the network configuration shown in FIG. 8, and a plurality of
border nodes are used as pathways.
In such a network configuration, the routing search process
described above is executed until the same border node is reached,
but sometimes the search is not executed for the nodes of all
networks even when the paths shown by the arrows are obtained. In
this case, improvement of the efficiency of routing search is
achieved in consideration of the allowance of the costs.
For this purpose, simply a path of the lowest cost is previously
obtained without considering the restrictions in wavelengths and
the like at all. Then the lowest cost, which is simply obtained
beforehand, is compared with the cost of a path which is searched
in the above-described routing search process until the same border
node is reached. As a result of this comparison, if the lowest
cost, which is simply obtained beforehand, is within the allowance
(within 120%, for example), this obtained path is taken as the
lowest cost path in accordance with the flow shown in FIG. 11,
without considering that the searching may not be performed for the
nodes of all networks. The path search can be continued only when
the allowance is exceeded.
As described above, in the network in which the ROADM and the like
are connected to the mesh network in a multi-stage manner, it is
necessary to consider a plurality of wavelengths in a plurality of
subnetworks present at the output side of the network, thus a
routing computation graph for the number of wavelengths is
required. However, according to the present invention, such a
routing computation graph for the number of wavelengths is no
longer necessary, as described in the embodiments with reference to
the drawings. Thus, even if the number of multiplexed wavelengths
increases drastically to the hundreds, increase of the memory
capacity for execution of routing computation can be avoided,
whereby large industrial contribution is realized.
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